The present invention relates to sensor devices and, more particularly, to an implantable bio-sensor system that includes an electro-active polymer (EAP) generator which is specifically adapted to provide substantially continuous and reliable power to the bio-sensor system as a result of mechanical flexing of the EAP generator in response to movement of muscle within which the EAP generator may be embedded.
Blood glucose concentration level of a patient is normally controlled by the pancreas. However, for patients suffering from diabetes, the pancreas does not properly regulate the production of insulin as needed to metabolize food into energy for the individual. For diabetic patients, glucose levels must be checked or monitored several times throughout the day so that insulin may be periodically administered in order to maintain the glucose concentration at a normal level. In one popular method, the glucose level is monitored by first obtaining a sample of blood from finger-pricking.
The glucose level of the blood sample is then placed on a glucose measurement strip and a subsequent chemical reaction produces a color change that may be compared to a reference chart. In this manner, the reaction of the blood sample with the glucose measurement strip provides an indication as to whether the glucose level is abnormally low or high such that the diabetic patient may administer the proper amount of insulin in order to maintain the glucose concentration within a predetermined range. Such administration of insulin is typically performed by way of self-injection with a syringe.
Unfortunately, the finger-pricking method of glucose testing is uncomfortable as both the blood-pricking and the insulin injections are painful and time-consuming such that many diabetic patients are reluctant to check their glucose levels at regular intervals throughout the day. Unfortunately, glucose levels often fluctuate throughout the day. Therefore, even diabetic patients who are otherwise consistent in checking their glucose levels at regular intervals throughout the day may be unaware of periods wherein their glucose levels are dangerously low or high. Furthermore, the finger-pricking method is dependent on patient skill for accurate testing such that the patient may rely on erroneous data in determining the dosage level of insulin. Finally, self-monitoring of glucose levels imposes a significant burden on less capable individuals such as the young, the elderly and the mentally-challenged.
At the time of this writing, it is estimated that 17 million people in the United States, or about six percent of the population, have diabetes. Due in part to dietary habits and an increasingly sedentary lifestyle, particularly among children, diabetes is expected to increase at the rate of about 7 percent every year such that the disease is predicted to eventually reach epidemic proportions. In addition, the current cost of diabetes in the United States alone is estimated at over $120 billion with the total U.S. sales of the glucose measuring strips alone estimated at about $2 billion. Thus, there is a demand for continuous, reliable and low-cost monitoring of glucose levels of diabetic patients due to the increasing number of people diagnosed with diabetes.
Included in the prior art are several implantable devices that have been developed in an effort to provide a system for continuous glucose monitoring. In some of the prior art implantable devices, an electrochemical sensor may be used to measure glucose concentration levels. Such sensors may use an amperometric detection technique wherein oxidation or reduction of a compound is measured at a working electrode in order to determine substance concentration levels. A potentiostat is used to apply a constant potential or excitation voltage to the working electrode with respect to a reference electrode.
When measuring glucose concentration levels in the blood, glucose oxidase (GOX) is typically used as a catalyst. Upon applicaiton of the excitation voltage to the working electrode, the GOX oxidize glucose in the patient's blood and forms gluconic acid, leaving behind two electrons and two protons and reducing the GOX. Oxygen that is dissolved in the patient's blood then reacts with GOX by accepting the two electrons and two protons to form hydrogen peroxide (H2O2) and regenerating oxidized GOX. The cycle repeats as the regenerated GOX reacts once again with glucose.
The consumption of O2 or the formation of H2O2 is subsequently measured at the working electrode which is typically a platinum electrode. As oxidation occurs at the working electrode, reduction also occurs at the reference electrode which is typically a silver/silver chloride electrode. The more oxygen that is consumed, the greater the amount of glucose in the patient's blood. In the same reaction, the rate at which H2O2 is produced is also indicative of the glucose concentration level in the patient's blood. In this manner, the electrochemical sensor measures the glucose concentration level.
Unfortunately, such implantable devices of the prior art suffer from several deficiencies that detract from their overall utility. One such deficiency is that implantable devices may expend a substantial amount of power in sensing and processing sensor signals. The power requirement for such devices necessitates the use of large batteries in order to prolong the useful life. Implantable devices having large batteries as the power source may require periodic surgeries for replacement of the batteries when the capacity drops below a minimum level. Furthermore, large batteries may contain large amount of hazardous chemicals or substances that may present a risk of harm to the patient due to toxicity of such substances which may leak into the patient after implantation.
Also, due to the relatively limited power capacity of batteries, the range of functions that may be performed by the implantable device may be somewhat limited. For example, it may be desirable to monitor multiple physiological parameters in addition to glucose concentration levels of the patient. In such cases, the implantable device may include multiple sensors wherein each sensor simultaneously monitors a different physiological parameter of the patient. For example, in addition to monitoring glucose concentration levels, the temperature and heart rate of the patient may also be monitored. Unfortunately, a device having multiple sensors may consume more power than can be supplied by a battery that is miniaturized to a size that is small enough for use in an implantable device.
As can be seen, there is a need for an implantable bio-sensor system that overcomes the above-described deficiencies associated with powering the bio-sensor system. More specifically, there exists a need in the art for an implantable bio-sensor system that is not solely dependent upon batteries for power. There also exists a need in the art for an implantable bio-sensor system that provides an essentially unlimited or continuous power supply such that multiple sensors may allow for simultaneous and selective monitoring of multiple physiological parameters of the patient.